How to care for houseplants during a heat wave

During the recent heat wave, green thumbs likely made plans to care for their outdoor gardens with enough water and other measures.

But what about your houseplants? Houseplants, like their garden-planted siblings, can suffer in excessive heat, whether from the outside temperature or the air conditioner.

So that you’re prepared for the next heat wave, here are some tips on keeping indoor plants healthy, from Emily Griswold, a director of horticulture at the UC Davis Arboretum and Public Garden.

How often should I water plants during a heat wave?

The equation is simple: When it is hotter, plants need more water. Container plants may need daily or twice-daily watering in extreme heat, according to Iowa State University.

Experts recommend watering plants in the early morning or evening, when it’s cooler and less water will evaporate. However, “if your plant is dry, and the only time you can water it is 2 p.m., give your plant water,” Griswold said.

Overwatering is still possible in hot weather, and some plant diseases thrive in hot, wet conditions, Griswold cautioned. Gardeners should follow the usual rule of thumb: Check the soil in the plant’s pot, as deep as is possible, and only add water if it is dry.

Bottom watering is another good option for potted plants during a heat wave, said Karen Mitchell, a Purdue University College of Agriculture consumer horticulture extension specialist.

To do this, place a pot — with a hole in it — in a layer of water about an inch deep. Let it soak, allowing the roots to suck up the moisture and distribute it throughout the soil, until the soil feels moist toward the top of the pot when you touch it with your finger — usually between 10 minutes and an hour, depending on the size of the plant.

How do I protect my plants from the air conditioner?

Air conditioners can dry out plants and soil, and are an additional reason to be vigilant with watering and misting during a heat wave. Keeping plants out of the direct path of an air conditioning vent is advised.

One option can be to move plants to rooms with higher humidity, such as the bathroom or kitchen, during times of heightened air conditioner use, Griswold said.

According to Bloomscape, an indoor plant company, other options include using a humidifier, grouping plants together around a dish of water or using a pebble tray. To do this, place a layer of pebbles in a shallow tray, add water until the pebbles are almost covered and put the plant pot on top.

How can I reduce heat stress in plants?

Along with dryness, a major concern during a heat wave for plants is sunburn, in which leaves lose their color and become brittle. This is especially a concern for plants with broad leaves that have a lot of surface area.

The simplest way to avoid this is to move a plant out of direct sunlight when the temperature spikes, whether it has been placed outdoors, on a balcony or by a window. If the plant cannot be moved, then the sun can be blocked with a shade covering — even an umbrella, Griswold said.

She added that a plant with burned leaves is not necessarily a lost cause, and if it is watered and removed from the sun, eventual new growth can appear. “Plants are quite resilient,” she said. “If it hasn’t gone beyond what’s called the permanent wilting point, it can still revive.” A drip irrigation system, to slowly and deeply soak the soil, is one recommended treatment for a heat-stressed plant, she added.

Adding mulch around the roots of a container plant increases its resilience in hot weather, Griswold said, because it helps the plant conserve moisture and regulates the temperature of the soil.

Signs of heat stress include leaves rolling, cupping, wilting and drying around the edges, according to Oregon State University. It recommends against making changes such as spraying chemicals, fertilizing, pruning or replanting in extreme heat.

Spraying herbicides and pesticides can exacerbate sun scorch, experts at the Missouri Botanical Garden warn. Try to avoid spraying your plants during a heat wave, or move them out of the sunlight to do so.

What are some recommended heat-resistant and heat-tolerant plants?

Succulents, cactuses and aloes, which naturally grow in hot and dry environments, are a safer bet for surviving in hot weather. Other options, according to Good Earth Plant Company, a San Diego-based business, include pothos or Devil’s Ivy, umbrella plants, geraniums and ponytail palms.

Griswold said that a useful general rule, as the world gets hotter, was to look at plants that thrive to the south of where you are, for those in the Northern Hemisphere. “In California, we’re looking more to Baja California and the desert southwest,” she said. “And if you were in the northeast, you might be looking to the southeast for ideas.”